During the formation of a star, a circumstellar disk is also formed, where gas and dust abound. A planetary system around this young star should be assembled out of this disk, so we also call this disk a protoplanetary disk. However, from interstellar dust grains to newborn planets, planet formation covers 30 orders of magnitude in mass and 13 orders of magnitude in size. The process involves complicated interactions between the solid materials, the gaseous medium, the stellar irradiation, and the magnetic field (see the PPVII chapter by Lesur et al. 2022). Therefore, despite the thousands of extrasolar planetary systems already detected (see NASA Exoplanet Exploration), indicating the ubiquity of planets around stars, we still do not have a comprehensive picture of how planets are born.
A chief objective in my research is to comprehend the formation of kilometer-scale planetary objects, also known as planetesimals, directly from dust grains in realistic protoplanetary disks. This process remains one of the most challenging stages in the theory of planet formation (see the review by Birnstiel, Fang, & Johansen 2016). Direct growth of interstellar μm-sized dust grains by mutual collisions suffers from poor sticking properties, so the grains can only bounce from each other without further growth, or even destroy each other at high-speed collisions. Moreover, the grains constantly feel headwind in the disk as they orbit around the star, so they lose angular momentum and quickly drift towards the star in a short time compared to the life of a protoplanetary disk. Therefore, before they can form planetesimals, these grains need to somehow concentrate themselves to high density such that the collective gravity of the grains becomes strong enough to take over the process.
Not surprisingly, it remains extremely difficult to model a protoplanetary disk that captures many of the physical processes mentioned above. For this reason, computational astrophysics has been playing an essential role in the studies of protoplanetary disks and planet formation. In particular, we conduct large-scale computer simulations of protoplanetary disks which contain interacting dust particles and gas, and study their dynamics in a turbulent environment. The resulting data analyses help us understand the structure of protoplanetary disks and the conditions for planetesimal formation, which should shed more light on recent and future observations of resolved protoplanetary disks as well as the formation history of the Solar and the extrasolar planetary systems.
A chief objective in my research is to comprehend the formation of kilometer-scale planetary objects, also known as planetesimals, directly from dust grains in realistic protoplanetary disks. This process remains one of the most challenging stages in the theory of planet formation (see the review by Birnstiel, Fang, & Johansen 2016). Direct growth of interstellar μm-sized dust grains by mutual collisions suffers from poor sticking properties, so the grains can only bounce from each other without further growth, or even destroy each other at high-speed collisions. Moreover, the grains constantly feel headwind in the disk as they orbit around the star, so they lose angular momentum and quickly drift towards the star in a short time compared to the life of a protoplanetary disk. Therefore, before they can form planetesimals, these grains need to somehow concentrate themselves to high density such that the collective gravity of the grains becomes strong enough to take over the process.
Not surprisingly, it remains extremely difficult to model a protoplanetary disk that captures many of the physical processes mentioned above. For this reason, computational astrophysics has been playing an essential role in the studies of protoplanetary disks and planet formation. In particular, we conduct large-scale computer simulations of protoplanetary disks which contain interacting dust particles and gas, and study their dynamics in a turbulent environment. The resulting data analyses help us understand the structure of protoplanetary disks and the conditions for planetesimal formation, which should shed more light on recent and future observations of resolved protoplanetary disks as well as the formation history of the Solar and the extrasolar planetary systems.